In general, to adjust the size of a hole of a work material that has been pre-bored with a drill or to smooth the inner peripheral surface of the hole, a reaming operation is performed such that the inner periphery of the hole is cut with a shallow cutting allowance by use of a reamer that is a cutting tool and that has a plurality of slender blades (in most cases, six or eight blades) protruded from the periphery of its head. In recent years, a machine reamer in which blades made of a hard tool material, such as super-hard alloy, ceramic, or cermet, are fixed to, for example, a steel-made reamer head body in accordance with the kind of a work material or machining conditions has been widely used as a machine reamer (chucking reamer) to be attached to a main rotational shaft of a machine tool, instead of a machine reamer in which the whole of the tool or the whole of its head is made of a single tool material, such as high-speed steel. Especially, a machine reamer having blades made of super-hard alloy or cermet has been most widely used.
Recently, the whole of cutting operations has been required to have high accuracy and high efficiency, and a reaming operation has been likewise required to be heightened in processing efficiency. However, a conventional machine reamer has advantages and disadvantages resulting from the material of blades of the machine reamer, and hence the requirements have not been fully satisfied. For example, a machine reamer having blades made of super-hard alloy can be used for heavy cutting since the cutting edge of the blade has high toughness. However, since an increase in peripheral velocity allows a work material to be easily melted and adhered to the blade, it becomes difficult to perform a high-speed reaming operation. Additionally, the cutting edge of the blade is relatively quickly worn down, and its life is shortened. On the other hand, a machine reamer having ceramic blades is great in the hardness of the cutting edge of the blade, and hence the peripheral velocity can be heightened. However, since the cutting edge is brittle and is liable to be easily broken, it is difficult to use the ceramic blade for heavy cutting. Additionally, a machine reamer having cermet-made blades is merely intermediate between super-hard alloy and ceramic in performance, such as processing speed, durability, or cutting load resistance, because cermet exhibits intermediate properties between the properties of super-hard alloy and the properties of ceramic in toughness and hardness.